1. Field of the Invention
The present invention relates to a belt transmission apparatus for transmitting a rotating force using a belt when an engine is started, or when an accessory is driven to operate by means of an engine.
2. Description of the Related Art
A typical example of such a belt transmission apparatus is disclosed in Japanese Patent Application Laid-Open No. 8-14145. The belt transmission apparatus disclosed therein includes a crank pulley mounted on a crankshaft of an engine, auxiliary pulleys respectively mounted on accessories arranged around the engine, a starter pulley attached to a starter motor, and a belt arranged to wrap around these pulleys to operatively connect them one another in such a manner that a driving force is transmitted from the starter motor through the belt to the engine to start it during engine starting, whereas a driving force is transmitted from the engine through the belt to the respective accessories to drive them after the engine has been started.
As a large transmission torque is required when the engine is started by the conventional starter motor through the belt, it is necessary to apply a high tension to the belt, but in this case, there arises a problem in that the belt is continuously subjected to the high tension unnecessarily even after the engine has been started, thus resulting in a remarkable reduction in the usable service life of the belt.
Moreover, in cases where the high tension is applied to the pulleys mounted on the accessories, there also arises another problem in that it is necessary to increase the strength of the shaft and bearings supporting the pulleys of the accessories, as well as the strength of the support structures therefor, thus increasing the sizes and costs of the accessories.